A hard disk drive (HDD) is a storage drive used for storing and retrieving digital information. A HDD generally has one or more rapidly rotating disks with a magnetic head arranged on a moving actuator arm to read and write data to the disk surface. A typical disk is spun at speeds varying anywhere from 4,200 rpm in energy-efficient portable devices, to 15,000 rpm for high performance servers. Other disks may spin at 1,200 rpm, 3,600 rpm, or in the range of 5,400 rpm to 7,200 rpm, though any range of speeds could be used.
Due to the extremely close spacing between the magnetic head and the spinning disk surface, HDDs are vulnerable to being damaged by a head crash—a failure of the disk in which the head scrapes across the platter surface, often grinding away the thin magnetic film and causing data loss. Head crashes can be caused by, among other things, electronic failure, a sudden power failure, physical shock, contamination of the drive's internal enclosure, wear and tear, corrosion, or poorly manufactured disks and heads.